The molecular mechanisms of invertebrate phototransduction and invertebrate retinal degeneration are to be investigated. The studies focus on a test of the capacitative Ca2+-entry hypothesis and make use of Drosophila mutants with defects in genes encoding ion channels that appear to be necessary for refilling intracellular Ca2+ stores. Three lines of research are proposed. One is to transform flies with mutant forms of the trp gene to analyze structure/function relationships. Another line of investigation is to determine more directly the effects of the TRP mutations by expressing and analyzing the mutant proteins in oocytes. The third area of investigation is to monitor Ca2+ uptake and release in preparations of fly eye microsomes. Information from these studies is to be applied to the understanding of degeneration observed in certain Drosophila mutants.